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We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us?

Answer: Because the range of frequency for each vibrating body varies. However, because humans can hear vibrations in the range... View Article

We have two identical metal sheets. One of them is rubbed with sandpaper and the other with ordinary paper. The one rubbed with sandpaper shines more than the other. Give reason.

Answer: Frictional force refers to the force generated by two surfaces that contact and slide against each other. Friction is... View Article

What are the possible expressions for the dimensions of the cuboids whose volumes are given below? Volume : 12ky² + 8ky – 20k

Answer: The cuboid shape is a closed 3d figure that is enclosed by rectangular faces that means plane regions of... View Article

What are the possible expressions for the dimensions of the cuboids whose volumes are given below? Volume : 3x² – 12x

Answer: The cuboid shape is a closed 3d figure that is enclosed by rectangular faces that means plane regions of... View Article

What Happens To Light When It Gets Dispersed? Give An Example.

The splitting of white light into its constituent colours is called dispersion. During dispersion, the white light is spread into... View Article

What happens when (a) Dilute sulphuric acid is poured on a copper plate? (b) Iron nails are placed in a copper sulphate solution? Write word equations of the reactions involved.

Answer: (a) No reaction occurs when dilute sulphuric acid is poured on a copper plate. However, when concentrated sulphuric acid... View Article

What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.

Answer: Sewage is wastewater that is discharged from residences, hospitals, industries, offices, and other locations. Rainwater that runs down the... View Article

What kind of lens is there in our eyes? Where does it form the image of an object?

Answer: Our eyes have a convex lens that focuses light on the back of the eye, on a layer called... View Article

What planning is required in advance to deal with the situation created by a cyclone?

Answer: Cyclone is defined as the mass of air that rotates around the centre of low pressure on a large... View Article

What precautions would you take if lightning occurs while you are outside the house?

Answer: Lightning can be explained in terms of charges produced due to rubbing. During a thunderstorm, the air currents move... View Article

When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.

Answer: Physical change – A substance is said to undergo a physical change when only the physical properties such as... View Article

When a glass rod is rubbed with a piece of silk cloth the rod (a) and the cloth both acquire positive charge. (b) becomes positively charged while the cloth has a negative charge. (c) and the cloth both acquire negative charge. (d) becomes negatively charged while the cloth has a positive charge.

Answer: (b) becomes positively charged while the cloth has a negative charge. When the glass rod is rubbed with silk... View Article

When an electric current is passed through a conducting solution, there is a change of colour of the solution. This indicates (a) the chemical effect of current. (b) the heating effect of current. (c) the magnetic effect of current. (d) the lightning effect of current.

Answer: (a) the chemical effect of current. Electrical conductors are materials that allow electricity to flow through them easily. If... View Article

When are the maximum and minimum temperatures likely to occur during the day?

Answer: Cloudy, sunny, rainy, stormy, or clear weather all are possibilities. It is a natural occurrence that keeps the atmosphere... View Article

When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.

Answer: When baking soda and lemon juice are mixed, carbon dioxide gas is produced, resulting in bubbles. This is a... View Article

When carbon dioxide is passed through lime water, it turns milky due to the formation of _________.

Answer: When carbon dioxide is passed through lime water, it turns milky due to the formation of Calcium carbonate. When... View Article

When the cutting edge of a knife is put against a fast rotating stone to sharpen it, sparks are seen to fly. Explain the reason.

Answer: Frictional force refers to the force generated by two surfaces that contact and slide against each other. Friction is... View Article

When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

Answer: The deflection of the compass needle indicates that current is flowing through the wire. When the free ends of... View Article

When we hear a sound, does any part of our body vibrate? Name the part.

Answer: When we hear a sound our eardrum vibrates. Sound enters through the outer part of the ear, travels down... View Article

Whenever the surfaces in contact tend to move or move with respect to each other, the force of friction comes into play (a) only if the objects are solid. (b) only if one of the two objects is liquid. (c) only if one of the two objects is gaseous. (d) irrespective of whether the objects are solid, liquid or gaseous.

Answer: (d) irrespective of whether the objects are solid, liquid or gaseous. Frictional Force Friction is the force that resists... View Article

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